The present invention relates to a method for fabricating semiconductor device, more specifically, a method for fabricating a semiconductor device including ferroelectric capacitors.
Recently, the use of ferroelectric film as the dielectric films of the capacitors is noted. The FeRAM (Ferroelectric Random Access Memory) using such ferroelectric capacitor can operate at high operating speed and has low electric power consumption. The FeRAM is a non-volatile memory characterized by good write/read durability, etc. and prospects for further development.
However, the ferroelectric capacitor has a characteristic that the characteristics are easily deteriorated by hydrogen gas or water from the outside. Specifically, for the ferroelectric capacitor of a standard FeRAM, having the lower electrode of Pt film, the ferroelectric film of PZT film and the upper electrode of Pt film sequentially stacked, it is known that when the substrate is heated to a temperature of about 200° C. in an atmosphere of an about 40 Pa (0.3 Torr) hydrogen partial pressure, the PbZr1-XTiXO3 film (PZT film) substantially loses the ferroelectricity. It is known that when the substrate is subjected to heat treatment with the ferroelectric capacitor adsorbing sufficiently water or with water being present near the ferroelectric capacitor, the ferroelectricity of the ferroelectric film of the ferroelectric capacitor is much deteriorated.
Because of this characteristic of the ferroelectric capacitor, in the FeRAM fabrication process, a process which generates water as little as possible and is made at low temperatures is selected as the process following the formation of the ferroelectric film. As the process for forming the inter-layer insulation film, a film forming process by CVD (Chemical Vapor Deposition) or others using a raw material gas which generates a relatively small amount of hydrogen is selected.
Furthermore, as the technique for preventing the deterioration of the ferroelectric film by hydrogen or water are proposed the technique of forming a barrier film of aluminum oxide film covering the ferroelectric capacitor and the technique of forming a barrier film of aluminum oxide film on an inter-layer insulation film formed on the ferroelectric capacitor. The barrier film of aluminum oxide, film has the function of preventing the diffusion of hydrogen or water. Accordingly, the proposed techniques can prohibit hydrogen or water from arriving at the ferroelectric film and prevent the deterioration of the ferroelectric film due to the hydrogen or water.
However, the barrier film simply formed on an inter-layer insulation film having steps in the surface does not have good coverage and cannot sufficiently prevent the diffusion of hydrogen or water. When hydrogen or water arrives at the ferroelectric film of the ferroelectric capacitor, the metal oxide forming the ferroelectric film is reduced with the hydrogen, and the electric characteristics of the ferroelectric capacitor are deteriorated.
Then, a technique of planarizing the surface of the inter-layer insulation film and forming the barrier film on the planarized inter-layer insulation film is proposed. The flat barrier film has very good coverage and can surely prevent the diffusion of hydrogen or water.
Following references disclose the background art of the present invention.
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Specification of Japanese Patent Application Unexamined Publication No. 2005-217044
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However, when the flat barrier film is formed on the inter-layer insulation film, the conductor plugs buried in the inter-layer insulation film are not formed well, and the fabrication yield is often lowered.